This invention relates to a process for selectively equilibrating a C.sub.3 or greater monoalkene to a hydrocarbon mixture using a HAMS-1B crystalline borosilicate-based catalyst composition in which the production of total butylenes and t-amylenes is substantially enhanced. More particularly, this invention relates to the selective gas-phase equilibration of at least one C.sub.3 or greater monoalkene over a HAMS-1B crystalline borosilicate-based catalyst composition to a largely olefin mixture employing operating conditions which maximize the n-butenes and isobutylene portion of the C.sub.4 fraction and the t-amylene portion of the C.sub.5 fraction and minimize the formation of C.sub.1 to C.sub.3 hydrocarbons, total aromatics, and total paraffins; such mixture is usefully separated in one aspect of the invention by reaction with methanol to form the methyl ethers of isobutylene and the t-amylenes.
The commercial preparation of olefins involves thermally cracking a hydrocarbon feedstock such as gas oil, naphtha, or an ethane-propane combination. With each of these feedstocks propylene is a major product and accompanies other olefins and diolefins, such as ethylene and butadiene, and additional hydrocarbons. The particular distribution of products for a given feedstock is relatively fixed which can lead to overproduction of one olefin product to meet the demand for another product or products from the cracking process. Thus, it is desirable to develop "add-on" processes which can be utilized in conjunction with the thermal cracking process to convert a product produced in market excess to other products in shorter supply and of more commercial value. Unlike the thermal cracking process, such "add-on" processes need to be catalytic since they should be selective in converting the excess product.
In particular, it is of advantage to be able to economically convert propylene when it is in long supply to higher value products useful in the transportation fuel industry since the transportation fuel market is enormous and can absorb large quantities of suitably converted excess "cracker" propylene. If propylene could be converted economically to a process stream rich in total butylenes and t-amylenes, diversion of the excess propylene to the gasoline market is possible since new regulations covering the amount of lead in gasoline have forced refiners to seek new sources of octane, one of which is the methyl ethers of isobutylene and t-amylenes, MTBE and TAME, respectively. The methanol required to make these ethers is inexpensive and plentiful and the isobutylene and t-amylenes are generally the limiting components. In addition, linear butenes are the preferred feedstock for the acid catalyzed alkylation of isobutane to make high octane fuel supplements. Thus, a process to convert propylene selectively to total butylenes and t-amylenes could have substantial economic value.
Now, catalyzed equilibration processes have been found to selectively convert propylene and higher olefins to largely olefin products containing a high proportion of total butylenes and t-amylenes while reducing the formation of total paraffins and C.sub.1 -C.sub.3 hydrocarbons. These processes when combined with existing technology for conversion of isobutylene and t-amylenes to their methyl ethers and n-butenes to "alkylate" can economically convert propylene and other olefins to valuable products having an essentially unlimited market.
A number of processes for catalytically processing olefins have been taught in the past; for example, in U.S. Pat. No. 4,451,685 a process is described to convert propylene to gasoline blending stock which comprises contacting an AMS-1B crystalline borosilicate-based catalyst with C.sub.2 -C.sub.3 olefins. The C.sub.2 -C.sub.3 olefins are converted to a mixture of alkanes, alkenes, branched alkanes and alkenes, and aromatics useful as a gasoline blending stock. Olefin interconversion product distributions resulting from propylene conversions over HZSM aluminosilicate zeolites as a function of space velocity and temperature are described at p. 109 in "Catalysis by Intermediate Pore Zeolites," an article in the Proceedings of the Second Symposium of the Industry--University Cooperative Chemistry Program of the Department of Chemistry, Texas A&M University, Apr. 1-4, 1984. In U.S. Pat. No. 4,503,282, a process to convert a substantially linear alkene, such as n-butene, to isomerized products is taught, which process comprises contacting such alkene at a temperature above about 300.degree. to about 650.degree. C. and an alkene reactant partial pressure of less than about 0.4 atmospheres with an AMS-1B borosilicate-supported catalyst containing at least 50 weight percent hydrogen form AMS-1B. As the described process is an isomerization, essentially all the products have the same carbon number as the starting alkene. A method to convert an alkene to oligomerized, aromatized, or isomerized products over an AMS-1B borosilicate-based catalyst system is taught in U.S. Pat. No. 4,499,325. Methods are taught by which linear butenes, for example, can be converted to isobutylene, dimerized to C.sub.8 products and converted to aromatics. Converting organic compounds over a catalyst comprising a zeolite of altered activity resulting from reacting the zeolite either "as synthesized" or initially ion exchanged, with a compound having a complex fluoroanion which could include a fluoroborate is taught in U.S. Pat. No. 4,500,421. In U.S. Pat. No. 4,456,779, processes of converting pressurized liquid olefins to a mixture containing a high proportion of C.sub.5 + hydrocarbons in the gasoline boiling and distillate range are taught. Such processes are carried out over an acid ZSM-5 type catalyst. The processing of light olefins (2 to 4 carbon atoms) to products comprising either high octane olefin gasoline components or high octane aromatic gasoline components is taught in U.S. Pat. No. 4,150,062. U.S. Pat. No. 4,456,582 teaches the preparation and use of molecular sieves including a borosilicate for catalytic purposes including propylene oligomerization to mixtures containing aromatics, aliphatics, and, primarily, C.sub.5 to C.sub.9 olefins. In U.S. Pat. Nos. 2,242,530, 4,307,254, and 4,336,407, a method of reacting and separating isoolefins from hydrocarbon mixtures using combined reaction (with methanol) and distillation is taught. C.sub.4 and C.sub.5 isoolefins are among those taught as useful in this catalytic distillation process.